Iraq's power grid is on the brink of collapse because of insurgent sabotage, rising demand, fuel shortages and provinces that are unplugging local power stations from the national grid, according to officials.

Aziz al-Shimari, an electricity ministry spokesman, said at the weekend that power generation nationally was only meeting half the demand, and there had been four nationwide blackouts over the past two days. The shortages across the country were the worst since the summer of 2003, shortly after the US-led invasion to topple Saddam Hussein, he added.

Power supplies in Baghdad have been sporadic all summer and now are down to just a few hours a day at most. The water supply in the capital has also been severely curtailed by power blackouts and cuts that have affected pumping and filtration stations.

Kerbala province, south of Baghdad, has been without power for three days, causing water mains to go dry in the Shia holy city of Kerbala, the provincial capital.

Hazim Obeid, who sells clothing at a Kerbala market stall, said: "We no longer need television documentaries about the stone age. We are actually living in it. We are in constant danger because of the filthy water and rotten food we are having."

Electricity shortages are a perennial problem in Iraq, even though it sits atop one of the world's largest crude oil reserves. The national power grid became decrepit under Saddam Hussein because his regime was under UN sanctions after the Gulf war and had trouble buying equipment to upgrade the system.

The power problems are only adding to the misery of Iraqis, already suffering from the effects of more than four years of war and sectarian violence. Outages make life almost unbearable in the summer months, when average daily temperatures reach between 43.3C (110F) and 48.8C.

One of the biggest problems facing the national grid is the move by provinces to disconnect their power plants from the system, reducing the overall amount of electricity being generated for the entire country. Provinces say they have no choice because they are not getting as much electricity in return for what they produce, mainly because the capital requires so much power.

"Many southern provinces - such as Basra, Diwaniya, Nassiriya, Babil - have disconnected their power plants from the national grid. Northern provinces, including Kurdistan, are doing the same," Mr Shimari said. "We have absolutely no control over some areas in the south.

"The national grid will collapse if the provinces do not abide by rules regarding their share of electricity. Everybody will lose and there will be no electricity winner," Mr Shimari said.

He complained that Baghdad was unable to stop provincial power stations pulling out of the national system or provinces failing to take themselves off the grid once they had used their daily ration of electricity. Compounding the problem, Mr Shimari said of 17 power lines running into the capital, only two were operational. The rest had been sabotaged.

Fuel shortages are also a major problem. Ghalib al-Daami, a provincial spokesman in Kerbala, said a 50-megawatt power station had been shut down due to a lack of fuel, leaving the entire province without water and electricity for three days.

He said sewage was seeping above ground across nearly half the city because pumping trucks used to clean septic tanks had been unable to operate due to petrol shortages. The sewage was causing a health threat to citizens and contaminating crops in the region.

Many people who would normally rely on small, home generators for electricity could not afford to buy fuel. Petrol prices had shot up to nearly 65p a litre, Kerbala residents said, a price that put the fuel out of range for all but the wealthy.

"We wait for the sunset to enjoy some coolness," said Qassim Hussein, a 31-year-old labourer in Kerbala. "The people are fed up. There is no water, no electricity, there is nothing but death. I've even had more trouble with my wife these last three days. Everybody is on edge."

Iraq has the world's third-largest proven oil reserves, behind Saudi Arabia and Iran. But oil production has been hampered by insurgent and saboteur attacks, ranging from bombing pipelines to siphoning off oil. The attacks have cost the country billions of dollars since the 2003 US invasion. Dilapidated infrastructure has also hindered refining, forcing Iraq to import large amounts of kerosene and other oil products.